Recent progress in RF superconductivity

The wide spread activities to prepare major size superconducting accelerating systems mainly for the large storage rings presently under construction in Europe and Japan are based on the continuous progress in rf superconductivity achieved in the past years. The thermal stability of s.c. cavities has been increased significantly by improving the thermal conductivity of niobium with different techniques. The promising attempts to sputter high purity niobium onto 500 MHz copper cavities have shown encouraging results. Multicell cavities at 3 GHz coated with Nb3Sn achieved high Q values already at 4.2 K. Field emission studies using modern surface analytical tools are shedding more light on anomalous electric surface breakdown fields. This report summarizes briefly the current activities in different laboratories and comments on recent achievements with superconducting cavities and in materials research. It concentrates on work performed prior to the preparation of accelerator experiments. These are discussed by R. Sundelin and in other contributions to this conference